The aim of this study is to propose a stratigraphic and sedimentary framework though the integration of available sedimentary, diagenetic and petrophysical data, which will be utilized in the construction of a high resolution stratigraphic framework, as an input into comprehensive review and update of an existing model of heterogeneous carbonate reservoir in a mature field in Abu Dhabi, UAE.
Depositional facies have been defined in cored wells, subsequently were associated taking into account the biologic and sedimentary processes in response of carbonate growing and sea level changes, allowing the identification of the main stratigraphic surfaces.
Surfaces can extend the correlation along the field and define the model of facies that, with the evidence provided by cores, can recreate and predict the different regressive-transgressive cycles in high resolution which the carbonate platform were undergone during its evolution.
Diagenetic evolution, interpreted through laboratory observations, was integrated with facies and petrophysical evaluation allowing the understanding of the spatial distribution of petrophysical properties within a heterogeneous reservoir and define a new set of facies which will be used in the generation of geological static model.
Application of sequence stratigraphy methods in cores, and extended in logs allowed the identification of six depositional sequences, with thicknesses of 2 to 4 meters each, corresponding to the phases of carbonate platform growth. Within each depositional sequences, typical cycles were defined that support the understanding in the association of facies and their relationship during the deposition.
The identification of sedimentological cycles not only genetically organizes the facies and predicts the stacking pattern, but also makes possible to find an excellent correspondence between cycles from lowstand system track intervals with good to excellent permeability values, and cycles from transgressive system track intervals with low permeabilities.
Many of the sequence stratigraphy published articles driven for the most important reservoirs along the Arabian Plate, provide an excellent tool in the regional correlation. However, they are not enough to be used in the reservoir characterization in detail that is required during the development of the field neither as input data in the generation of geological static models that use the sedimentary trends as constrain to populate the petrophysical properties.
The prediction of the spatial distribution of petrophysical properties within heterogeneous reservoirs are affected by significant uncertainties when based only on well information. However, integrating additional constraints such as 3D seismic data and sedimentary concepts can significantly improve the accuracy of reservoir models and help reduce uncertainties on predictions away from wells.
The aim of this study is to build a reliable 3D geological static model through an integrated workflow using petrographic and sedimentary reports and the current understanding of the sedimentary conceptual model for the field in order to reduce the uncertainty. These core interpretations provide a clear description of the facies architecture across the A-Field, serving as excellent reference during seismic stratigraphy interpretations and lead into a geological distribution of the petrophysical properties in the reservoir through the facies models.
An integrated approach for facies modeling was implemented in order to generate stochastic models of the facies associations capable to reproduce the natural transition through the sequences. This method was adopted to model the high-resolution prograding pulses in the carbonate platform that were interpreted through cores description and facies association interpretation for both reservoirs.
The final 3D sedimentary-stratigraphic architecture is used as main constrain to model the petrophysical properties for each reservoirs. Under this approach, these models can account for varying the spatial continuity of reservoir properties honoring the different sedimentary facies. Facies-based property models preserve the facies-specific statistical distribution of the property, as well as its depositional direction. The facies-based 3D petrophysical models provide an improved prediction of petrophysical properties distribution and reservoir heterogeneity. The permeability simulation based on facies and the cloud transform between porosity and permeability allows better control of spatial connectivity patterns across the reservoir that could be used for improving reservoir performance predictions as it was carried out in the present static model.
Laverde, Fabio (Schlumberger) | Pozo, Gerardo (PETROBRAS Energia Peru) | Miranda de Oliveira, Flavio (PETROBRAS Energia Brazil) | Carrillo, Gonzalo (Schlumberger) | Torres, Kevin Michael (PETROBRAS Energia Peru) | Sanchez, William (Schlumberger) | Alvarez B., Jose Luis (PETROBRAS Energia Peru) | Contreras, Fabio (Schlumberger)
Block X, located in the Talara Basin in northwest Peru, is one of the oldest producing basins in America. The reservoirs that have been studied are the Eocene Mogollon, Ostrea, Echinocyamus, and Helico units. The present structural model has benefited from previous jobs performed by Petrobras, where an old extensive fault system oriented northeast to southwest was affected by a later fault system trending northwest to southeast. Low-angle faults have cut the upper section of the Helico unit, consequently moving older sequences to the northwest. This structural setting controls the distribution of facies bodies, their interaction, size, and geometry, and the quantity of sand facies.
Based on an integrated facies analysis from numerous outcrops, 21 cored wells and more than 750 well-log motifs, a reliable stratigraphic framework was constructed that resulted in the identification of specific facies associations, stratigraphic or depositional surfaces, defining genetic units . Gross depositional fluvio-deltaic environments of the Mogollon succession were interpreted toward the southeast, shoreface at the Ostrea facies throughout the area, the deltaic and fluvial for the Echinocyamus in localized areas, and the tidal flat-beach-coastal plain toward the northeast, with the important development of fan deltas into submarine canyon-fills. This development was recorded within the Helico at the southwest of the study area. Because of the many years of production data available, the geologic model and facies distribution could be adjusted with dynamic data, such as pressure data, production tests and water cut. A possible way of achieving such conditions included adjusting the connectivity between sand bodies, their orientation and the vertical communication.
The products of the integrated study included: 1) mapped areas and zones of potential reservoir connectivity, and 2) geological model building used in 3D geostatic modeling. Mapping of the sequences resulted in the proposal of new infill wells and potential workovers. The results of the 3D static model work were: a) realistic fine-scale geological models that were consistent with the observed data, b) calculations of uncertainties in the oil-in-place volume.